This invention relates generally to magnetic disk data storage systems, and more particularly to a magnetic write head design and methods for making same.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1A and 1B, a magnetic disk data storage system 10 of the prior art includes a sealed enclosure 12, a medium motor 14, a magnetic medium or disk 16, supported for rotation by a drive spindle S1 of the medium motor 14, an actuator 18 and an arm 20 attached to an actuator spindle S2 of actuator 18. A read/write head support system consists of a suspension 22 coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24.
The transducer 24 (which will be described in greater detail with reference to FIG. 1C) typically includes an inductive write element with a sensor read element. As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to "fly" above the magnetic disk 16. Alternatively, some transducers, known as "contact heads," ride on the disk surface. Discrete units of magnetic data, known as "bits," are typically arranged sequentially in multiple concentric rings, or "tracks," on the surface of the magnetic medium. Data can be written to and/or read from essentially any portion of the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in a short arc, as indicated by the arrows P, over the surface of the spinning magnetic disk 16. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 1C depicts a magnetic read/write head 24 including a read element 26 and a write element 28. A common surface known as the air bearing surface ABS in the plane 29, is shared by the read element 26 and write element 28. The magnetically active components of both the read element 26 and the write element 28 terminate at the ABS, which faces the surface of the magnetic disk 16 (see FIG. 1A). This configuration minimizes the distance between the magnetic medium 16 and the magnetically active components of the magnetic read/write head 24 for optimal reading and writing performance.
The read element 26 includes a first shield 30, an intermediate layer 32, which functions as a second shield, and a read sensor 34 that is located between the first shield 30 and the second shield 32. The most common type of read sensor 34 used in the read/write head 24 is the magnetoresistive (AMR or GMR) sensor which is used to detect magnetic field signals from a magnetic medium through changing resistance in the read sensor.
The write element 28 is typically an inductive write element. The write element 28 includes the intermediate layer 32, which functions as a first pole, and a second pole 38 disposed above the first pole 32. The first pole 32 and the second pole 38 are attached to each other by a backgap portion 40, with these three elements collectively forming a yoke 41. Above and attached to the first pole 32 at a first pole tip portion 43, is a first pole pedestal 42 exposed along the ABS. In addition, a second pole pedestal 44 is attached to the second pole 38 at a second pole tip portion 45 and is aligned with the first pole pedestal 42. This portion of the first and second poles 42 and 44 near the ABS is sometimes referred to as the yoke tip portion 46.
A write gap 36 is formed between the first and second pole pedestals 42 and 44 in the yoke tip portion 46. The write gap 36 is made of a non-magnetic material. This non-magnetic material can be either integral with (as is shown here) or separate from a first insulation layer 47 that lies below the second pole 38 and extends from the yoke tip portion 46 to the backgap portion 40.
Also included in write element 28 is a conductive coil 48, formed of multiple winds 49. Typically, the winds 49 of the conductive coil 48 spiral around the portion of the second pole near the backgap portion 40 in a plane that is substantially perpendicular to the viewing plane of FIG. 1C. Some designs in the prior art employ several substantially parallel conductive coils arranged in a stack, rather than the single conductive coil 48 illustrated. For ease of viewing, complete winds are not shown.
The conductive coil 48 is positioned within a non-magnetic and electrically insulating medium 50 that lies above the first insulation layer 47. As is well known to those skilled in the art, current passed through the conductive coil 48 magnetizes the yoke 41 and creates a magnetic field across the write gap 36 between the first and second pole pedestals 42 and 44. The magnetic field across the write gap 36 can induce a reorientation of magnetic domains in a nearby magnetic medium such as a magnetic disk 16 (see FIG. 1A). Changing the magnetic field across the write gap 36 as the write gap 36 is moved relative to, and in close proximity with, a magnetic medium 16 can induce corresponding variations in the orientations of magnetic domains within the magnetic medium along the write element path of travel. The smallest region on the surface of the magnetic disk 16 that may be induced to have coherently oriented magnetic domains typically constitutes a single bit. By this process bits may be sequentially written along a track on the surface of the magnetic disk 16.
In FIG. 1D, a view taken along line 1D--1D of FIG. 1C further illustrates the structure of the read/write head 24. As can be seen from this view, the first and second pole pedestals 42 and 44 have substantially equal widths of Wp which are smaller than the width W of the first and second pole tip portions 32 and 38 in the yoke tip portion 46.
Of critical importance to the disk drive industry is the total quantity of information that can be written within a unit area on the surface of a magnetic disk 16. This quantity is sometimes referred to as the areal density and is typically expressed in terms of bits per square inch. The number of bits per square inch is a function of two primary factors: how many bits can be written within a unit length of a track, known as the linear density and expressed as bits per inch; and how many tracks can be placed within a unit area, known as the track density and expressed as tracks per inch. The linear density and the track density are each functions of several variables.
The linear density is a function of the length of the bits and the spacing between them, and is maximized by making the bits smaller and placed closer together. To maintain data integrity, though, bits cannot overlap. One of the problems in the prior art that limits the ability to place bits closer together is a phenomenon sometimes referred to as the second pulse effect. The second pulse effect is a problem whereby the process of writing a bit on a track actually produces two bits, a first intended bit closely followed in the track by a second unintended bit. Ordinarily, the second unintended bit is smaller than the first bit and the two bits may be distinguished on this basis. However, the very presence of the second unintended bit close behind the first intended bit precludes writing another intended bit in the unintended bit's place. Thus, these spurious unintended bits created by the second pulse effect can limit how closely legitimate intended bits may be written in a track.
The track density is a function of the trackwidth, which is also the width of the individual bits written within the track, and the spacing between the tracks. Maximization of track density is achieved by making bits narrower and by reducing the spacing between tracks. The width of a written bit is essentially a function of the dimensions of the write element at the ABS and the distance between the ABS and the magnetic disk 16. For example, in the write element of FIGS. 1C and 1D, the width is a function of the pole pedestals 42 and 44 dimensions. The spacing between tracks in theory could be completely eliminated so that the edges of adjacent tracks just touch one another. In practice, however, mechanical tolerances, such as the accuracy with which the arm 20 may be positioned, limit how closely tracks may be placed without having adjacent tracks undesirably overlap one another. Another limitation known in the art is a phenomenon sometimes referred to as side-writing. Side-writing is a problem whereby the process of writing bits to the magnetic disk 16 additionally creates spurious features adjacent to the bits but outside of the track. Consequently, if tracks are placed too near one another, these spurious features created by the side-writing phenomenon may overlap the bits on adjacent tracks. When the problem of side-writing is present, tracks may need to be placed still further apart than required by mechanical tolerance considerations.
The causes of side-writing and the second pulse effect may be related to the relative arrangement of the poles and the pole pedestals. More specifically, flux leakage at the interface between the second pole pedestal 44 and the second pole tip portion 45 may induce the second pulse effect, and flux leakage directly from the edges of the second pole tip portion 45 to the first pole tip portion 43 may create undesirable side-writing. Together, these two effects can hamper efforts to achieve higher areal densities.
Accordingly, what is desired is an easily fabricated write element that significantly reduces both side-writing and the second pulse effect to allow for higher linear densities and higher track densities thereby achieving greater areal densities.